In an image display device, for example, a cathode ray tube display device (CRT), a plasma display panel (PDP), an electroluminescence display (ELD), a vacuum fluorescent display (VFD), a field emission display (FED) or a liquid crystal display device, it is suitable to provide an optical film which is transparent and has an antistatic property and a hardcoat property in order to prevent breakage or scratch and to prevent reduction in visibility due to attachment of dust or the like on the display surface or destruction of the display device due to static electricity. In particular, in response to a resent trend, for example, upgrade in quality, increase in size, decrease in thinness or extension in lifespan to the image display device, it is requested for the optical film which is applied to the image display device to have good other performances in addition to the hardcoat property and antistatic property, and high durability.
Particularly, in a liquid crystal display device, it is suitable to use an optical film having a good balance between the hardcoat property and the antistatic property as a protective film for polarizing plate, and in order to maintain a good adhesion property to a polarizer in the form of polarizing plate, a cellulose acylate film is ordinarily used as a base material of optical film.
From the standpoint described above, the cellulose acylate film needs to have high transparency (low haze), good moisture permeability and good optical performances and it is adjusted heretofore to fulfill the performances by adding a specific plasticizer. However, a phosphate ester, for example, triphenyl phosphate (TPP), which is a typical plasticizer, sublimates in a drying step during the production of cellulose acylate film and thus, the contamination attached to the production line falls down onto the film to cause a problem of surface state failure or the like. In addition to the problem above, from the standpoint of providing a protective film for polarizing plate which is environmentally friendly and a method of producing thereof, it is required that the phosphate ester is not used as the plasticizer for cellulose acylate film.
It is known that a sugar or a derivative thereof is suitable in the use of plasticizer used in a cellulose film for optical film, and of the sugar and derivatives thereof, an example using a sugar ester compound is known (JP-A-2001-247717 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and WO 2009/031464).
Also, in order to obtain an optical film having both the antistatic property and the hardcoat property, it is known to form an antistatic hardcoat layer using a composition containing an ion conducting polymer, for example, a quaternary ammonium salt group-containing polymer as an antistatic agent and a polyfunctional monomer to form a binder (for example, JP-A-2009-263567).